LNIDA, there is a difference between " social taxes" that provide for basic health services, fire brigade, pensions etc and " employment taxes" that are at a much higher rate. The contractor must pay the " employment taxes" at the appropriate rate based on where the majority of their duties start and they are normally responsible for their accommodation. If you are UK based this will work out to about 40% and in Spain about 37%. I understand from NAS that the agency that employs you pays the 7% social tax but that you must provide a ' tax certificate" showing the employment taxes being either paid, either at you home base or in another country in which case only " differential tax" between your operating base and the country you pay tax in is collected. In short, this is not a " tax free" job and NAS are keen to avoid the mess the RYR pilots got into which may come back to haunt the company.